CT及MRI在诊断小肠原发尤文肉瘤/原始神经外胚层肿瘤中的价值一例并文献回顾

韩旭1,2,张挽时3,孙美玉2

1.大连医科大学 研究生院,辽宁 大连116044;2.大连医科大学附属第一医院放射科,辽宁 大连 116011;3.空军总医院磁共振科,北京市 100142

[摘 要]目的 探讨小肠原发尤文肉瘤/原始神经外胚层肿瘤 [(Ewing’S Sarcoma,ES)/(Primitive Neurotodermal Tumour,PNET)]的CT、MRI特征诊断及鉴别诊断。方法 对1例小肠ES/PNET患者的CT、MRI影像表现结合病理及免疫组化进行分析 ,并回顾相关文献。结果 患者女性,15岁,贫血两年,间断便血1月余。CT示右下腹小肠肿块,密度不均;增强 病灶实性成分不均匀强化。MRI示肿块呈等长T1、T2信号,增强特点与CT相同。病理示浆膜层小圆细胞恶性肿瘤伴出血囊变,肿瘤细胞呈弥漫及巢状排列,血窦丰富;免疫组化分化抗原99(CD99)(++)、波形蛋白(VIM)(+)、突触素(Syn)(+)、上皮膜抗原(EMA)(弱+)、孕激素受体(PR)(+)、人角蛋白抗原决定簇5.2(CAM5.2)(弱+)。结论 小肠ES/ PNET是一种罕见小圆细胞恶性肿瘤,CT、MRI表现无特异性,但可以准确定位和描述肿瘤的大小、形态、密度,明确其恶性征象及有无远处转移,为术前诊断及手术方案制定提供大量重要信息。

[关键词]CT;MRI;小肠;尤文肉瘤/原始神经外胚层肿瘤;免疫组化

引言

尤文肉瘤(Ewing’S Sarcoma,ES)最初被认为是一种儿童未分化骨肉瘤,现在与原属于软组织的原始神经外胚层肿瘤(Primitive Neuroectodermal Tumour,PNET)联系在一起,构成一个家族,并以ES/PNET统一命名。这些肿瘤都具有低分化的小圆细胞的形态学特征[1],包括典型ES,骨外ES,外周神经外皮瘤及胸肺部PNET(Askin tumor)[2-4]。好发于颈部、腹部、腹膜后腔、骨盆和胸壁,发生于小肠的病例十分罕见[5]。神经源性标记物CD99(MIC2)CD99(糖蛋白MIC2)及波形蛋白通常是过度表达的[6-8]。我们查阅大量相关文献,报道发生于消化道的ES/PNET的并不多见,对其影像学表现的报道就更为罕见,主要报道于小样本量研究或是病例报道。回顾先前报道过的ES/P NET的影像特征[1,5,9-17],在CT平扫上肿块呈稍低密度,其内可见坏死囊变区,少于10%的肿瘤内可见钙化[10],增强扫描呈不均匀强化,囊性成分不强化;MRI影像上肿块通常表现为T1WI呈等、低信号,T2WI不均匀高信号,增强扫描呈不均匀强化。其影像表现特异性较差,易误诊为胃肠道的其他恶性肿瘤或其他类型小圆细胞肿瘤,如胃肠道间质瘤(Gastrointestinal Stromal Tumor,GIST)、成神经细胞瘤、淋巴瘤、横纹肌肉瘤等。以下我们将通过对一例小肠ES/PNET的影像特点的分析,并探讨CT及MRI检查在该疾病术前诊断中的应用价值。

1 资料与方法

1.1 一般资料

患者,女性,15岁,因贫血2年,间断便血1月余入院,无既往史及家族史。常规实验室检查,糖类抗原CA125值为50.5 U/mL。

1.2 仪器与方法

CT扫描仪器采用Somatom Def i nitim Siemens双源螺旋CT,① 检查前准备:患者在检查前禁食8~12 h,饮水1500 mL,以充分充盈胃肠道;② 常规CT定位扫描,范围包括膈肌至骼嵴;③ 患者取仰卧位,屏气以减少伪影。采用高压注射器经肘前静脉注射非离子型对比剂优维显(370 mgI/mL),剂量按1.0~1.5 mL/kg体质量计算,流率4 mL/s。常规行三期扫描(分别在静脉注射后25~30 s,60~80 s和120~180 s行动脉期、静脉期和延迟增强扫描)。扫描参数:管电压120 kV,管电流180 mA,扫描速度0.5 s,探测器64×0.6,螺距0.9,图像扫描层厚8 mm。

MR扫描仪器采用Siemens Avanto 1.5T扫描仪,全景成像矩阵(Total Imaging Matrix,TIM)线圈,患者取仰卧位。三维定位后:① 横断面常规T1加权成像(TR/TE:500/7.9 ms)、轴位T2加权成像(TR/TE:3900/88.46 ms)和矢状位压脂T2加权成像(TR/TE:7829/82.84 ms);②弥散加权成像(Diffusion Weighted Imaging,DWI),应用二维平面回波弥散加权序列(EPI2DWI)技术,取扩散敏感系数b值为50、300、600 s/mm2;③ 经静脉注射对比剂(Gd-DTPA),注射剂量为0.01 mmol/kg,行横断面及矢状位Flex-LAVA增强成像(TR/TE:4.2/2.0 ms),各序列成像层厚4~7 mm,层距1 mm,激发次数1次,视野260 mm× 440 mm,矩阵224×320。

2 结果

2.1 CT表现

全腹CT平扫及增强检查示:右下腹部第6组小肠局限性管壁增厚,并向腔内突出不规则软组织肿块,其内可见片状低密度区,病灶表面凹凸不平,密度欠均匀,累及范围约8.5 cm×14.4 cm(冠状位测量);增强扫描病灶实性成分呈不均匀明显强化(图1)。

图1 全腹CT扫描表现

注:a~b.平扫,第6组小肠处不规则软组织肿块,其内片状低密度,病灶表面凹凸不平;c.增强扫描动脉期,病灶实性成分呈不均匀明显强化。

2.2 MR表现

盆腔MRI平扫及增强检查示:右下腹-子宫膀胱陷凹见等长T1、等长T2囊实混杂性肿块,边界清晰,范围约7.3 cm×5.3 cm×10.0 cm。增强扫描肿块呈不均匀明显强化,囊性成分未见强化(图2)。

2.3 免疫组织化学染色结果

免疫组织化学染色结果:免疫组化分化抗原99(CD99)(++)、波形蛋白(VIM)(+)(图3)、突触素(Syn)(+)、上皮膜抗原(EMA)(弱+)、孕激素受体(PR)(+)、人角蛋白抗原决定簇5.2(CAM5.2)(弱+)。

2.4 手术及病理结果

术中所见:行小肠肿物根治术,术中腹腔内见淡血性腹水,量约100 mL;小肠全长约5 m,距离回盲瓣约160 cm处小肠有约15 cm×8 cm×6 cm大小肿瘤,包膜完整,向腔外生长,分叶状,未见明显破溃,与周围肠管、附件无粘连;滋养血管粗大,系肠系膜上动脉分支血管。

术后病理:浆膜层可见小圆细胞恶性肿瘤伴出血、囊性变;肿瘤细胞呈弥漫及巢状排列,血窦丰富,大小:10.5 cm×5.5 cm×5.2 cm,残端未见肿瘤,结合免疫组化,考虑ES/PNET(图4)。

图2 盆腔MRI扫描

注:a.T1WI,病灶以等、高信号为主;b~c.常规T2WI轴位及压脂T2WI矢状位,示病灶呈混杂性高信号;d~f.T1WI增强,病灶明显不均匀强化,边界清晰。

图3 免疫组织化学染色

注:a.CD99(+);b.VIM蛋白(+)。

图4 肿瘤组织病理

注:a.镜下见小圆细胞恶性肿瘤,肿瘤细胞弥漫排列;b.肿瘤细胞呈巢状排列;c.肿瘤细胞血窦丰富。

3 讨论

外周原始神经外胚层肿瘤是一组拥有相似的细胞遗传学和生物特征高级别小圆细胞肿瘤[4],好发于颈部、腹部、腹膜后腔、骨盆和胸壁,发生于小肠的病例十分罕见[5]。CD99(糖蛋白MIC2)和波形蛋白通常过度表达[6-8],对本病的诊断有一定的特异性,本例也符合,可发生于任何年龄,儿童及青年多见[9]

Khong等[1]对7例发生在不同部位的外周ES的影像表现进行分析,发现在CT图像上所有7例肿瘤相对与肌肉均呈等或稍低的密度,中心可见更低密度区,符合囊性改变,CT增强扫描均呈不均匀强化;其中有6例进行MR扫描,图像示肿瘤在T2WI上表现为不均匀高信号,其中4例肿瘤在T1WI上信号不均匀,中心见囊变区,5例肿瘤在增强时呈明显强化。Ibarburen等[10]对17例外周尤文肉瘤患者的CT和MRI影像分析发现与其他类型的软组织肉瘤影像表现鉴别,并无特异性影像特征,仅表现出较大的肿块,边界欠清兼具浸润性。Kushener等[11]发现40%的病例中可发现坏死或出血区,反映了本病侵袭性的本质。Tan等[12]对36例不同部位的外周PNET影像特征进行分析显示,所有病例均未见远处转移,仅3例发生淋巴结转移,然而既往文献报道[18]外周PNET患者常发生远处转移,淋巴结转移者较少见,导致这种差异的原因可能与患者早诊断,并及时手术治疗有关。Wang等[17]对15例骨外PNET患者进行5~24个月时间不等的随访,7例经外科切除的患者中有6例复发并远处转移,7例行放化疗治疗者中有4例复发并远处转移,1例未行治疗者6个月后出现远处转移。

起源于胃肠道的ES/PNET影像表现报道较罕见。文献报道过的ES/PNET在CT平扫时常呈稍低密度,内部可见坏死囊变区,增强扫描囊性成分不强化;MRI扫描时表现为等T1、不均匀长T2信号,增强扫描呈不均匀强化。因ES/PNET的影像表现特异性差,故易误诊为胃肠道的其他恶性肿瘤或其他类型小圆细胞肿瘤,需鉴别于GIST,成神经细胞瘤,淋巴瘤,横纹肌肉瘤等。本例首诊为小肠恶性间质瘤,胃肠道间质瘤是消化道最常见的原发性间叶组织源性肿瘤,最常见于胃,小肠次之[19];在CT及MRI上表现为密度不均匀的软组织肿块,其内可有出血、坏死、囊变区[20]。成神经细胞瘤,多见于5岁以下儿童,最常见于腹部;其次是纵隔,85%的病灶CT的特征性表现为瘤体内见沙粒样钙化,增强不均匀强化[21];淋巴瘤,是腹膜后最常见的肿瘤,主要影像表现为腹膜后类圆形软组织肿块,钙化和坏死少见,边界清晰,增强扫描表现为轻度均匀强化[22];横纹肌肉瘤(Rhabdomyosarcoma)是儿童期最常见的软组织肿瘤,约占儿童期恶性肿瘤的4.5%[23-24],表现为腹腔或腹膜后较大略低密度软组织肿块,CT增强动脉期其内见血管穿行,静脉期呈片絮状强化。

4 结论

由于胃肠道ES/PNET十分罕见,很难实现大量的病例采集及统计分析,是本报道的不足之处。本例ES/PNET起源于右下腹第6组小肠,在CT平扫上肿块形态不规则,呈等密度,肿块内部有囊变坏死区,增强扫描病灶实性成分明显强化,囊性成分不强化;MRI扫描,肿块表现为囊实混杂信号,在T1WI呈等、低信号,T2WI呈等、高信号,边界清晰,增强扫描肿块呈不均匀明显强化,囊性成分无强化,与既往文献报道的外周ES/PNET影像特征相仿。因其不具备影像特异性,故难以做出精确诊 断,当我们评价小肠肿瘤时,可将其作为一种罕见的鉴别诊断。但通过影像学检查可以对肿块准确定位和描述病灶大小、形态、密度,并确定肿瘤的恶性征象及有无远处转移,可以为术前诊断及手术方案的制定提供大量有价值的信息。若要对此类肿瘤进行精确诊断及分类还需要综合免疫组化和细胞学检查。

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本文编辑 聂孝楠

Application Value of CT and MRI in Diagnosis of Ewing’s Sarcoma/Primitive Neuroectodermal Tumor: A Case Report and Literature Review

HAN Xu1,2, ZHANG Wan-shi3, SUN Mei-yu2

1.Department of Graduate School, Dalian Medical University, Dalian Liaoning 116044, China; 2.Department of Radiology, the First Affiliated Hospital of Dalian Medical University, Dalian Liaoning 116011, China; 3.Department of MRI, Air Force General Hospital, Beijing 100142, Chi na

Abstract:Objective To investigate CT and MRI feat ures, diagnosis and antidiastole of Ewing’s Sarcoma/primitive neuroectodermal tumor (ES/PNET) in small intestine. Methods Analysis CT and MR imaging feature, with pathology and immunohistochemistry of 1 case of small intestinal ES/PNET patient and review of the literature. Results A 15-year-old female patient with two-year history anemia and interm ittent hematochezia for 1 month. CT scan revealed the presence of a large soft tissue mass in right l ower abdomen, the mass was heterogeneous. A contrast enhanced CT scan demonstrated that the solid components of the mass were obvious enhanced. The MRI scan revealed that a heterogeneous mass arose in r ight lower abdomen-vesicouterine pouch, which presented isointensity on both T1-weight image and T2-weight images. The enhancement pattern of the mass was similar i n MRI with that of CT scans. The pathology diagnosis was altered to intestine malignant small round cell tumor with blood sinus, areas of hemorrhage and cyst formation can be seen, the cells were diffuse and arranged in nests. Immunohistochemical tests were performed, the results were as follows: positive expression for CD99, VIM, Syn, EMA, PR and CAM5.2. Conclusion Small intestine ES/PNET is a rare small round and highgrade cell malignant tumors. The imaging feature are non-specif i c in CT and MRI, but the mass can be located accurately and described the size, shape and density. It also can conf i rm the signs of malignancy and whether there is a distant metastasis. It provides a great deal of valuable information for preoperative diagnos is and surgical planning.

Key words:CT; MRI; small intestine; ewings sarcoma/primitive neuroectodermal tumor; immunohis toehemistry

[中图分类号]R734.2;R445.4

[文献标识码]B

doi:10.3969/j.issn.1674-1633.2017.05.020

[文章编号]1674-1633(2017)05-0080-04

收稿日期:2016-12-20

修回日期:2017-01-15

通讯作者:张挽时,主任医师,研究方向为CT、MR影像诊断。

通讯作者邮箱:cjr.zhangwanshi@163.com